JP2007327919A - Surface potential measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface measuring device capable of measuring even a small surface potential, concerning a surface potential measuring device for measuring the surface potential of a measuring object. <P>SOLUTION: This surface potential measuring device for measuring the surface potential of the measuring object has a measuring electrode provided oppositely to the measuring object, a driving part for displacing the distance between the measuring object and the measuring electrode, and a measuring part for measuring the surface potential of the measuring object based on a voltage generated in the measuring electrode. The device has a characteristic wherein the driving part has a constitution for displacing the measuring electrode by a piezo actuator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface potential measuring device, and more particularly to a surface potential measuring device that measures a surface potential of a measurement target.

  A surface potential measuring device has been developed as a device for measuring static electricity on the surface of a semiconductor or an insulator. When measuring the surface potential of a measurement target, use a contact-type electrometer, such as a general tester or voltmeter, to measure the surface by contacting the probe with the measurement target. As a result, the surface potential cannot be measured in a state in which the object to be measured is charged. For this reason, non-contact type surface potential measuring devices have been developed (see, for example, Patent Documents 1 and 2).

  FIG. 5 shows a principle block diagram of a non-contact type surface potential measuring device.

The non-contact type surface potential measuring apparatus 10 is configured so that the measuring electrode 12 is opposed to the measuring object 11 in a non-contact state, and the measuring electrode 12 is displaced in the arrow Z direction, whereby the measuring electrode 12 and the measuring object 11 are displaced. The distance L is displaced. By displacing the distance L between the measurement electrode 12 and the measurement object 11, the capacitance between the measurement electrode 12 and the measurement object 11 changes, whereby an alternating current flows through the load _RL .

As a result, it is possible to measure the electric charge that is directly charged to the measurement object 11 in a non-contact manner. At this time, in the conventional surface potential measuring device 10, the electromagnetic vibration method and the tuning fork vibration method are used as the displacement method of the measurement electrode 12. In the electromagnetic vibration method and the tuning fork vibration method, the frequency of displacement of the measuring electrode 12 with respect to the measurement object 11, that is, the frequency of vibration was about 200 Hz.
JP 07-244103 A JP 2000-65878 A

  However, since the conventional surface potential measuring apparatus uses the electromagnetic vibration method and the tuning fork vibration method, the vibration of the measurement electrode 12, that is, the displacement frequency with respect to the measurement object 11 is 200 Hz.

The capacitance of the measurement object 11 and the measurement electrode 12 is C,
C = εS / d [F] (1)
ε: dielectric constant d: expressed by the distance between the measurement electrode and the measurement object.

Here, when the measurement electrode 12 is AC-oscillated with a sine wave sinωt, the capacitance C is
C = C _m · sinωt [f] (2)
C _m : can be expressed by a capacitance when the measurement electrode 12 is closest.

On the other hand, the current i flowing through the load _RL is
i = dQ / dt = (dv / dt) .multidot.C + (dC / dt) .multidot.E (3)
It can be expressed as

here,
(Dv / dt) · C = 0
Then, equation (3) becomes i = (dC / dt) · E (4)
It can be expressed as.

Here, assuming that the capacitance C of the equation (4) is the equation (2), the equation (4) is
i = ωC _m · cosωt · E (5)
It can be expressed as

Here, considering only the amplitude of the signal,
i = ωC _m · E (6)
It can be expressed as For this reason, the surface potential detectable from the equation (6) is determined by ω, that is, the vibration frequency.

  In the conventional surface potential measuring apparatus using the electromagnetic vibration method and the tuning fork vibration method, the vibration frequency is 200 Hz, and a surface potential of about several hundred volts can be measured.

  On the other hand, for semiconductor wafers and the like, it is required to measure a surface potential of several mV to several V generated by the manufacturing process, and conventional surface potential measuring devices cannot cope with it.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a surface measuring apparatus capable of measuring even a small surface potential.

  The present invention relates to a surface potential measuring device for measuring a surface potential of a measurement target, a measurement electrode provided opposite to the measurement target, a drive unit for displacing the distance between the measurement target and the measurement electrode, and the measurement electrode. And a measurement unit that measures the surface potential of the measurement object based on the voltage, and the drive unit is configured to displace the measurement electrode using a piezoelectric actuator.

  The drive unit has a drive circuit that drives the piezo actuator, the measurement unit is supplied with an amplification circuit that amplifies the potential of the measurement electrode, and a synchronization signal that is synchronized with the drive signal of the piezo actuator from the drive circuit. A phase detector that detects a phase difference from the output signal of the amplifier circuit, and an output circuit that outputs a signal corresponding to the surface potential of the measurement object based on the output signal of the phase detector. The measurement unit includes a feedback circuit that feeds back a feedback voltage corresponding to the output signal of the output circuit to the measurement electrode.

  Further, the present invention provides a surface potential measuring apparatus for measuring a surface potential of a measurement object, and is provided so as to be opposed to the measurement object, and a distance between the measurement object and the measurement electrode is changed. And a measurement unit that measures a surface potential of the measurement object based on a voltage generated in the measurement object, and the drive unit uses the piezoelectric actuator to measure the measurement electrode. It is the structure made to displace, It is characterized by the above-mentioned.

  The drive unit has a drive circuit that drives the piezoelectric actuator, the measurement unit is supplied with an amplification circuit that amplifies the potential of the measurement electrode unit, and a synchronization signal that is synchronized with the drive signal of the piezoelectric actuator from the drive circuit. And a phase detector for detecting a phase difference between the output signal of the amplifier circuit and an output circuit for outputting a signal corresponding to the surface potential of the measurement object based on the output signal of the phase detector. The measurement unit includes a feedback circuit that feeds back a feedback voltage corresponding to the output signal of the output circuit to the fixed electrode.

  According to the present invention, the surface which measures the surface potential of the measurement object based on the voltage generated at the measurement electrode by displacing the distance between the measurement electrode provided opposite to the measurement object by the drive unit and the measurement electrode and the measurement object. In the potential measurement device, by configuring the drive unit with a piezo actuator, the measurement electrode can be displaced at a high frequency, so that the output level can be increased, and thereby the measurement sensitivity can be improved.

  FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a drive unit of an embodiment of the present invention.

  The surface potential measuring apparatus 100 according to the present embodiment is an apparatus that measures a surface potential of a measurement target, and includes a measurement electrode 111, a driving unit 112, and a measuring unit 113. The measurement electrode 111 is provided to face the measurement object 101, and a distance L between the measurement electrode 111 and the measurement object 101 can be displaced by the driving unit 112.

  The drive unit 112 includes a piezo actuator 121, a driver 122, and an oscillation circuit 123.

  As shown in FIG. 2, the piezo actuator 121 includes a piezo element 151, a swinging member 152, an elastic member 153, and a case 154.

The piezo element 151 is made of an electrostrictive (electrostrictive) ceramic such as titanic acid, zirconic acid, lead (Pb (Zr, Ti) O ₃ ) or the like, and is laminated with electrodes interposed therebetween. By applying a voltage to this piezoelectric material, the piezoelectric material expands in the directions of arrows Z1 and Z2 due to the reverse piezoelectric effect. A drive signal is supplied from the driver 122 to the piezo element 151 and driven.

  One end of the piezo element 151 is fixed to the case 154, and a swing member 152 is attached to the other end. The case 154 is fixed to the fixing arm 161. A drive signal is supplied from the driver 122 to the piezo element 151. The piezo element 151 is driven by a drive signal supplied from the driver 122, and expands in the directions of arrows Z1 and Z2.

  When the piezo element 151 extends in the directions of arrows Z1 and Z2, the swing member 152 is displaced in the direction of arrow Z1. The swing member 152 is elastically pressed in the direction of the arrow Z2 by the elastic member 153. When the piezo element 151 returns to the original state, the swing member 152 returns to the direction of the arrow Z2.

  The elastic member 153 is composed of, for example, a disc spring, and elastically presses the swing member 152 against the swing member 152 in the arrow Z2 direction. An electrode part 141 is fixed to the tip of the swing part 152.

  The driver 122 divides the oscillation signal supplied from the oscillation circuit 123 into a desired frequency, generates a drive signal corresponding to the divided frequency, and supplies the drive signal to the piezo actuator 121. At this time, the driver 122 detects the amplitude of the piezo actuator 121 based on the applied voltage of the piezo actuator 121, and controls the piezo actuator 121 to be displaced with a desired amplitude. The driver 122 supplies a synchronization signal synchronized with the displacement of the piezo actuator 121 to the measurement circuit 113.

  The electrode part 141 is comprised from the insulating material, and the measurement electrode 111 is attached to the front-end | tip. A shield cover 142 is attached around the electrode portion 141. The shield cover 142 is grounded and prevents noise and the like from being mixed into the measurement electrode 111. The electrode part 141 is connected to the measurement circuit 113.

  The measurement object 101 is disposed so as to face the electrode unit 141. The measurement object 101 is, for example, an object made of a material that charges a surface such as a semiconductor or an insulator, and is placed on the fixed electrode 114 and its surface potential is measured. The fixed electrode 114 is made of a metal material or the like and is at a ground potential. As a result, the surface of the measuring object 101 becomes a potential based on the ground potential.

  The measurement circuit 113 includes a capacitor C, a preamplifier 131, a main amplifier 132, a phase detector 133, a DC amplifier 134, a display unit 135, an output circuit 136, and a feedback circuit unit 137.

  The measurement electrode 111 is connected to the preamplifier 131 via the capacitor C. The capacitor C supplies a signal obtained by cutting the DC component of the measurement electrode 111 to the preamplifier 131 as a detection signal. The preamplifier 131 amplifies the detection signal. The detection signal amplified by the preamplifier 131 is supplied to the main amplifier 132.

  The main amplifier 132 further amplifies the detection signal amplified by the preamplifier 131. The detection signal amplified by the main amplifier 132 is supplied to the phase detector 133.

  The phase detector 133 is supplied with a synchronization signal synchronized with the driving of the piezo actuator 121 from the driver 122, and outputs a DC signal corresponding to the phase difference between the detection signal and the synchronization signal. The DC signal detected by the phase detector 133 is a signal corresponding to the surface potential of the measurement target 101 and is supplied to the DC amplifier 134. The DC amplifier 134 DC amplifies the DC signal supplied from the phase detector 133.

  The signal amplified by the DC amplifier 134 is supplied as an output signal to the display unit 135, the output circuit 136, and the feedback circuit unit 137. The display unit 135 is constituted by a digital display panel such as an LCD, for example, and the surface potential of the measurement object 101 is digitized based on the output signal of the DC amplifier 134 and displayed on the display unit 135.

  The output circuit 136 outputs the signal amplified by the DC amplifier 134 from the output terminal Tout + as an output signal.

[Feedback circuit section 137]
FIG. 3 is a block diagram of the feedback circuit unit 137.

  The feedback circuit unit 137 includes a high voltage generator 161 and resistors R1 to R3.

  The high voltage generator 161 is supplied with the output signal amplified by the DC amplifier 134 and generates a high voltage corresponding to the output signal from the DC amplifier 134. The high voltage generated by the high voltage generator 161 is divided by the resistors R1 and R2, and applied to the measurement electrode 111 as a feedback signal through the resistor R3. The potential of the measurement electrode 111 is kept constant by the feedback signal from the feedback circuit unit 137, and the detection signal is stabilized, thereby stabilizing the measurement operation.

〔effect〕
According to the present embodiment, the measurement object 101 can be driven at a high frequency by using the piezo actuator 121 as the actuator of the drive unit 112 that displaces the measurement electrode 111 with respect to the measurement object 101. As a result, the measurement electrode 111 can be displaced with respect to the measurement object 101 at a high speed, so that a large detection signal can be obtained, and thus a minute potential can be detected.

  For example, when the frequency of displacement of the measuring electrode 111 is 1 kHz, a surface potential of about 1 mV to 1 V can be detected.

  As described above, according to the present embodiment, the surface potential of about 100 to 600 V, which was conventionally measurable, can be set to about 1 mV to 1 V, and thereby a low surface potential can be measured with high accuracy. It was. By using the surface potential measuring apparatus 100 of the present embodiment, for example, it is possible to measure even a small surface potential of several mV to several V such as semiconductor wear, and it can be applied to various fields.

[Other Examples]
FIG. 4 is a block diagram showing another embodiment of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  In the surface potential measuring apparatus 200 of the present embodiment, the measurement electrode 111 is fixed at a constant potential by a DC power supply 211, the fixed electrode 114 is connected to the measurement circuit 212, and the surface of the measurement object 101 is determined according to the potential of the fixed electrode 114. Measure the potential. Accordingly, since the detection signal can be acquired from the fixed electrode 114, the detection signal is not affected by the vibration, and the surface potential that is strong against the vibration can be measured. Therefore, the surface potential can be measured with high accuracy.

  The present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be realized without departing from the gist of the present invention.

It is a block block diagram of one Example of this invention. It is sectional drawing of the drive part of one Example of this invention. 3 is a block configuration diagram of a feedback circuit unit 137. FIG. It is a block block diagram of the other Example of this invention. It is a principle block block diagram of a non-contact type surface potential measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100, 200 Surface potential measuring apparatus 111 Measuring electrode, 112 Drive part, 113 Measuring part, 114 Fixed electrode 121 Piezo actuator, 122 Driver, 123 Oscillator circuit 131 Preamplifier, 132 Main amplifier, 133 Phase detector 134 DC amplifier, 135 Display 136 Output circuit, 137 Feedback circuit part 141 Electrode part, 142 Shield cover 151 Piezo element, 152 Oscillating member, 153 Elastic member, 154 Case

Claims (6)

In a surface potential measuring device that measures the surface potential of a measurement object,
A measurement electrode provided facing the measurement object;
A drive unit for displacing a distance between the measurement object and the measurement electrode;
A measurement unit that measures the surface potential of the measurement object based on a voltage generated in the measurement electrode;
The drive unit is configured to displace the measurement electrode by a piezoelectric actuator. The drive unit has a drive circuit for driving the piezo actuator,
The measurement unit includes an amplification circuit that amplifies the potential of the measurement electrode unit;
A synchronization signal that is synchronized with the drive signal of the piezo actuator is supplied from the drive circuit, and a phase detector that detects a phase difference between the synchronization signal and the output signal of the amplifier circuit;
The surface potential measuring device according to claim 1, further comprising: an output circuit that outputs a signal corresponding to the surface potential of the measurement object based on an output signal of the phase detector. The surface potential measuring device according to claim 1, wherein the measurement unit includes a feedback circuit that feeds back a feedback voltage corresponding to an output signal of the output circuit to the measurement electrode. In a surface potential measuring device that measures the surface potential of a measurement object,
A measurement electrode provided opposite to the measurement object and to which a constant potential is applied;
A drive unit for displacing a distance between the measurement object and the measurement electrode;
A fixed electrode in contact with the measurement object,
A measurement unit that measures a surface potential of the measurement object based on a voltage generated in the measurement object;
The drive unit is configured to displace the measurement electrode by a piezoelectric actuator. The drive unit has a drive circuit for driving the piezo actuator,
The measurement unit includes an amplification circuit that amplifies the potential of the measurement electrode unit;
A synchronization signal that is synchronized with the drive signal of the piezo actuator is supplied from the drive circuit, and a phase detector that detects a phase difference between the synchronization signal and the output signal of the amplifier circuit;
5. The surface potential measuring device according to claim 4, further comprising: an output circuit that outputs a signal corresponding to the surface potential of the measurement object based on an output signal of the phase detector. The surface potential measuring device according to claim 1, wherein the measurement unit includes a feedback circuit that feeds back a feedback voltage corresponding to an output signal of the output circuit to the fixed electrode.

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